1. Field of the Invention
The present invention relates to a stage apparatus for positioning an object, and more particularly to a reticle stage for an exposure apparatus.
2. Description of the Related Art
In a typical exposure apparatus, a stage apparatus is used for positioning a substrate or an original (hereinafter generically called a substrate). Japanese Patent Laid-Open No. 2004-079639 (corresponding to U.S. Pat. No. 6,903,468) discloses a stage apparatus that uses a repulsive force generated by permanent magnets for accelerating and decelerating a stage on which the substrate is placed.
The stage apparatus described in Japanese Patent Laid-Open No. 2004-079639 will be described below with reference to FIGS. 11A and 11B. A stage 104 on which a workpiece 103 is placed is guided by a guide 102 in the Y direction. The stage 104 is attached to movable members 105 of linear motors having fixed members 106 that are attached to a base (not shown). A force is generated between each movable member 105 and the corresponding fixed member 106, thereby driving the stage 104 in the Y direction.
Permanent magnets 109 are provided on the front and back sides of the stage 104 in a moving direction thereof. In addition, a pair of permanent magnets 112 that are vertically spaced from each other by a predetermined distance is fixed on the guide 102 at each side of the stage 104 in the moving direction thereof. The permanent magnets 109 and 112 are magnetized in the Z direction such that opposing surfaces thereof have the same pole. When the stage 104 is at either of its stroke ends and one of the permanent magnets 109 is placed between the corresponding pair of permanent magnets 112, a repulsive force that accelerates or decelerates the stage 104 is generated between the permanent magnets 109 and 112.
The above-described stage apparatus uses repulsive forces generated by the permanent magnets for accelerating and decelerating the stage. In such a stage apparatus, to set the stage in a standby state at a position where the repulsive force is applied thereto, a large force must be continuously generated by the linear motors during the standby period. When, for example, the stage apparatus is used as a reticle stage in an exposure apparatus, the stage is generally stopped at a position near a stroke end in a process of replacing a reticle. However, when a force sufficient to cancel the repulsive force is generated by the linear motors, heat is generated by the linear motors, which causes undesirable effects. In addition, the large force that is externally applied to the stage in the process of replacing the reticle can cause deformation of the stage or the reticle. These problems also occur when the stage position is initialized.